In a typical virtual display arrangement (e.g., see PCT patent application WO 99/52002 “Holographic Optical Devices” by Yaakov Amitai and Asher Friesem and U.S. Pat. No. 6,580,529 “Holographic Optical Devices” by Yaakov Amitai and Asher Friesem), the virtual image is typically formed by using several separate linear diffraction gratings. Using separate diffraction elements makes manufacturing of such grating assembly difficult and requires a precise definition of the grating period (e.g., typically two different grating periods are used) and an angle between the periodic lines. Furthermore, it requires a lot of space and the diffraction efficiency is usually dependent on polarization (e.g., strong or weak polarization).